This invention relates to a novel process for preparing d-.alpha.-(6-methoxy-2-naphthyl)propionic acid.
The d-.alpha.-(6-methoxy-2-naphthyl)propionic acid or its salt is useful as, for example, anti-flammatory or analgesic agents.
As processes for preparing d-.alpha.-(6-methoxy-2-naphthyl)-propionic acid, there have been heretofore known (i) a process in which aromatic modification of .alpha.-(6-methoxy-2-naphthyl)propionic acid is optionally resolved, (ii) a process in which an ester of d-.alpha.-(6-methoxy-2-naphthyl)-propionic acid is hydrolyzed in the presence of an acid catalyst, and the like.
The process in which racemic modification of .alpha.-(6-methoxy-2-naphthyl)propionic acid is optically resolved, however, can not be said to be a satisfactory one from an economical view point because it is necessary to repeat the crystallization several times or more and to use expensive agents for the optical resolution.
In the process in which an ester of d-.alpha.-(6-methoxy-2-naphthyl)propionic acid is hydrolyzed in the presence of an acid catalyst, the methoxy group at the 6-position in the naphthyl group of the carboxylic acid which is a desired product or of the unreacted starting ester tends to be partially converted to a hydroxy group by hydrolysis to form d-.alpha.-(6-hydroxy-2-naphthyl)propionic acid or its ester as a by-product, requiring treatment for purification after completion of the hydrolysis, and therefore the above process also can not be said to be a fully satisfactory one for an industrial application.
Further, there is known a process in which an ester of d-.alpha.-(6-methoxy-2-naphthyl)propionic acid is hydrolyzed in an organic solvent containing an alkali catalyst. In this process, however, racemization reaction occurs simultaneously with hydrolysis to result in remarkable decrease in the optical purity of the resulting product (see U.S. Pat. No. 4,417,070, Table 2 on page 4), and the process can be said not to be a good efficiency.